A fuel cell using polyelectrolyte allows a hydrogen-containing fuel gas and an oxygen-containing oxidant gas such as air to electrochemically react with each other, such that electric power and heat are produced at the same time. The fuel cell is basically structured with a polymer electrolyte membrane that selectively transports hydrogen ions, and paired electrodes formed on both the surfaces of the polymer electrolyte membrane, i.e., an anode and a cathode, respectively. The electrodes each have a catalyst layer whose principal component is carbon powder bearing platinum metal catalyst and which is formed on the front surface of the polymer electrolyte membrane, and a gas diffusion layer which has combined features of air permeability and electronic conductivity and which is disposed on the outer surface of the catalyst layer. Such an assembly made up of the polymer electrolyte membrane and the electrodes (including the gas diffusion layer) integrally joined and assembled is referred to as an electrolyte membrane electrode assembly (hereinafter referred to as the “MEA”).
Further, on the opposite sides of the MEA, electrically conductive separators for mechanically clamping the MEA to fix the same, and for establishing electrical connection in series between the MEA and adjacent MEA, are disposed, respectively. In each separator, at the portion being brought into contact with the MEA, gas flow channels for supplying corresponding electrode with a fuel gas or a reactant gas such as an oxidant gas, and to carry away generated water or excess gas are formed. Though the gas flow channels can be provided separately from the separators, such grooves are generally formed on the front surfaces of the separators to serve as the gas flow channels. It is to be noted that, such a structure body in which the MEAs are clamped between the paired separators is referred to as the “unit cell module”.
Supply of the reactant gas to the gas flow channels formed between the separators and the MEA and discharge of the reactant gas and generated water from the gas flow channels are each carried out in the following manner: through holes called manifold holes are provided at the edge portion of at least one of the paired separators, to establish communication between the inlet/outlet port of each of the gas flow channels and each of the manifold holes, and the reactant gas is distributed to the gas flow channels from the manifold holes.
Further, in order to prevent external leakage of the fuel gas or the oxidant gas supplied to the gas flow channels, or to prevent mixture of the gases of two types, gas sealing members or gaskets are disposed as sealing members between the paired separators, at the places where the electrodes are formed in the MEA, that is, around the external circumference of the power generation areas. The gas sealing members or the gaskets also seal the circumference of each of the manifold holes.
Because the fuel cell generates heat while driving, the cell must be cooled by coolant or the like, in order to maintain the cell at an excellent temperature state. Normally, a cooling portion for allowing the coolant to flow is provided every one to three cells. The general structure of a stacked battery (fuel cell stack) is as follows: the MEA and the separators, and the cooling portion are alternately stacked by ten to two hundred cells; thereafter, an end plate is disposed at each of the end portions of the whole cells having a current collecting plate and an insulating plate interposed therebetween, such that the whole cells are clamped between such paired end plates and fixed from both the ends through the use of fastening bolts (rods) or the like. As to the fastening method, the general method is to fasten with fastening bolts which are inserted into through holes formed at the edge portions of the separators; or to fasten up the entire stacked battery with a metal belt on the end plates.
With the stacked battery employing such a fastening method, it is regarded that it is important to fasten the unit cell module with a fastening force which is uniform in-plane (i.e., within a plane perpendicular to the stacked direction). This is because such a uniform fastening force makes it possible to prevent leakage of air, hydrogen, coolant and the like, and to prevent damage to the unit cell module. Further, consequently, it makes it possible to improve power generation efficiency, and to extend battery service life. In connection with such a fastening method, as shown in FIG. 12, Patent Document 1 proposes a method of fastening with bands 901 under a prescribed residual stress, from the viewpoint of the in-plane uniformization, minimization of bending load, and an improvement in air-tightness.
Similarly, Patent Document 3 discloses a method of fastening the entire stack with one band or two bands. Patent Document 4 discloses a method of fastening with a multitude of bands at both the side surfaces of the stack.
Further, as shown in FIG. 13, Patent Document 2 proposes a band fastening method in which fastening is carried out by metal bands 101 and auxiliary plates 102, and disk springs and bolts 103, so as to achieve a reduction in size and weight of the stack, which is highly reliable withstanding shock and vibration.
Further, Patent Documents 5 and 7 disclose fastening of the stack with bolts, in which a band and auxiliary plates are disposed so as to surround end plates at both the ends of the stack.
Still further, Patent Document 6 discloses fastening of the stack, in which six plate members disposed at respective planes of the stack are engaged with one another at their sides.